This invention is related to a travel control device for a vibrating plate compactor used for compacting paved road surfaces, and more particularly to a travel control device for a vibrating plate compactor wherein the rotational phase of one of two eccentric rotors rotating on a pair of parallel axes is changed relative to another eccentric rotor and the compactor is moved forward/backward by the synthesized vector thereof.
This type vibrating plate compactor generally known in the prior art has a pair of eccentric rotors, the rotational phase of one rotor being variable relative to the other rotor and its vector moving the device forward or backward. A device which uses hydraulic pressure to switch the travel direction forward or backward in order to change the rotational phase of an eccentric rotor is known from prior references such as Japanese Patent Kokai Nos. Sho 55/139884, Sho 63/60306, Hei 1/260107, and Hei 7/286306.
These known compactors are all provided with a spiral groove inside the driven gear on the driven shaft which is rotated by the drive shaft, and a piston rod having a pin to engage with the spiral groove of said driven gear inside said driven shaft. Common to these devices is the way in which the driven gear having the spiral groove is rotated by moving the piston rod in the axial direction and varying the rotational phase of the eccentric rotor on the driven shaft relative to the eccentric rotor on the drive shaft.
Among such compactors, that of Japanese Patent Kokai Sho 55/139884 is provided with a cylindrical driven gear and a piston rod and imparted the mechanical return force moving to one side of the cylindrical driven shaft on the piston rod by synthetic thrust of the rotor on the driven shaft and the rotor on the drive shaft imparts. The hydraulic pressure resisting the mechanical return force of the piston rod is applied from an outside source into the cylinder provided at one end of the cylindrical driven shaft, and by variably controlling the hydraulic pressure supplied, the position of the rotational angle of the driven gear can be selected to suitably change the phase of the eccentric rotor.
However, since a hand-held pump is used as a means to supply the oil into the cylinder provided at one end of the cylindrical driven shaft from the outside source to resist the mechanical return force trying to move toward one side of the cylinder of the piston rod in this conventional compactor, this type device requires large force to manually switch the pump to the opposite side from the position of the piston rod traveling with the fastest speed forward or backward against the largest mechanical return force. In large, heavy weight compactors, the switching operation becomes so heavy that it is impossible to operate the machine.
The compactor according to Japanese Patent Kokai Hei 1/260107 is provided with piston rods which can maintain the neutral state by springs on both sides inside the driven shaft, pistons and cylinders on both sides of the piston rod, connecting the cylinders and the outside pressure source to charge the pressure oil to one of the cylinders from the outside source to move the piston rod. This compactor is also problematic in that the hand-operated pump used for supplying pressure into respective cylinders requires large force and the switching operation is so heavy that heavy weight compactors cannot be used.
On the other hand, the compactor according to Japanese Patent Kokai Sho 63/60306 is provided with a piston and a cylinder at one end of the piston rod inside the driven shaft, and the cylinder is connected to a three-way switch valve in the direction of forward, backward and neutral positions and a hydraulic pump circuit to always return these valves to the neutral position by the spring force. The pressure of this hydraulic pump is used to supply pressure to the cylinder via the valves on the forward and backward sides. While this compactor is advantageous in that the switching operation requires small force and the speed can be controlled by the pressure oil charged to the cylinder at one end of the piston rod by the hydraulic pump, it is quite defective in that the switch valve always returns to the neutral position by the spring force. It is therefore impossible to hold the travel lever at a desired inclined position.
The compactor according to Japanese Patent Kokai Hei 7/286306 is similar to the compactor disclosed in Japanese Patent Kokai Hei 1/260107 in that is provided with a piston rod maintained neutral by springs on both sides in the driven shaft, and pistons and cylinders are respectively provided at both ends of the piston rod. A hydraulic pump circuit provided with a three-way valve which can be switched to the forward, backward and neutral directions is connected to both cylinders as an outside source to supply the oil from the valve to respective cylinders in order to switch the piston rod to any one of the three directions.
Although this compactor can reduce the force needed for switching because oil is supplied to cylinders at both ends of the piston rod by the hydraulic pump, all the oil from the pump is fed by switching the valve to the forward or backward directions to thereby set the fastest running speed in these directions. It is therefore impossible to set the running speed at an arbitrary speed.